Gastrointestinal absorption of a drug adminis- tered orally is affected by multiple parameters including drug dissolution rate, which is influenced by the drug solubility in gastrointestinal fluids.
Water solubility of an active pharmaceutical ingre- dient (API) is the critical factor in the design of solid oral dosage forms. Nowadays, approximately 40% of the immediate release dosage forms admin- istered orally contain active substances that are insoluble in water (1). Therefore, the low dissolu- tion rate of poorly soluble drugs, i.e., belonging to the class II and IV of the Biopharmaceutical Classification System (BCS), still remains one of the major problems in the formulation of the dosage forms. Many strategies can be applied to improve drug dissolution properties, namely:
micronization, formulation of solid dispersions, complexation with β-cyclodextrins or drug deriva- tization.
The liquisolid technique that has emerged in the last decade is a promising approach to the solu- bility improvement of poorly water soluble drugs.
Its main advantages include simplicity of manufac- turing, use of commercially available excipients,
and application of well-known methods and equip- ment utilized for the manufacturing of conventional tablets.
Liquisolid systems (LCS) are described as dry, free flowing and compressible powder mixtures with absorbed solution or dispersion of drug sub- stance in non-volatile solvent or liquid drug form (2). The liquisolid system is mainly composed of two groups of excipients: carriers and coating mate- rials. Various grades of microcrystalline cellulose (MCC), dibasic calcium phosphate, pregelatinized starch and lactose are commonly used as carriers, while different types of silica dioxide are utilized as coating material (3). The factor limiting formulation of reasonable size and low mass liquisolid tablets is the solubility of the active substance in non-volatile solvents. Thus, the application of solvents character- ized by high solubilizing capability could be a prom- ising method of reducing tablet size and mass. The most commonly used solvents include propylene gly- col, polyethylene glycol, polysorbate, CremophorÆ EL or SynperonicTMPE/L61 (4).
Insoluble model drug substances such as car- bamazepine, famotidine, furosemide, piroxicam and
OPTIMIZATION OF FUROSEMIDE LIQUISOLID TABLETS PREPARATION PROCESS LEADING TO THEIR MASS AND SIZE REDUCTION
MATEUSZ KUREK*, KRZYSZTOF WOYNA-ORLEWICZ, MOHAMMAD HASSAN KHALID and RENATA JACHOWICZ
Chair and Department of Pharmaceutical Technology and Biopharmaceutics, Jagiellonian University, Medical College, Medyczna 9, 30-688 KrakÛw, Poland
Abstract: The great number of drug substances currently used in solid oral dosage forms is characterized by poor water solubility. Therefore, various methods of dissolution rate enhancement are an important topic of research interest in modern drug technology. The purpose of this study was to enhance the furosemide dissolu- tion rate from liquisolid tablets while maintaining an acceptable size and mass. Two types of dibasic calcium phosphate (FujicalinÆ/EmcompressÆ) and microcrystalline cellulose (VivapurÆ 102/VivapurÆ 12) were used as carriers and magnesium aluminometasilicate (NeusilinÆ US2) was used as a coating material. The flowable liquid retention potential for those excipients was tested by measuring the angle of slide. To evaluate the impact of used excipients on tablet properties fourteen tablet formulations were prepared. It was found that LS2 tablets containing spherically granulated dibasic calcium phosphate and magnesium aluminometasilicate exhibit the best dissolution profile and mechanical properties while tablets composed only with NeusilinÆ US2 was char- acterized by the smallest size and mass with preserved good mechanical properties and furosemide dissolution.
Keywords: liquisolid, dissolution rate, furosemide, solubility
1325
* Corresponding author: e-mail: mateusz.kurek@uj.edu.pl; phone: +48 12 6205602, fax: +48 12 6205619
prednisolone have been used in the liquisolid tech- nology development (3-7).
A crucial limitation factor in the application of LCS technology is the dose of drug substance.
Javadzadeh et al. (6) suggested that the liquisolid method is suitable for dosages lower than 50 mg.
Nevertheless, it was found that the application of polymeric additives, e.g., polyvinylpyrrolidone (PVP) might help to overcome this problem, and higher amounts of drugs can be used. In that study, 100 mg of carbamazepine was loaded into liquisolid tablets weighting from 583 mg to 1010 mg per unit, but there is a lack of information about the size of the tablets (6). The application of excipients with high absorption capacity is another possibility to decrease the mass of the tablets. It was shown that application of porous excipients such as magnesium aluminometasilicate instead of conventional tablet- ing excipients resulted in an increased drug loading capacity of formulation (3). Despite the low dose of griseofulvin, 3 mg of the API had to be introduced in the form of 2 to 5 tablets with a diameter as big as 10 mm (8). The size and the mass of the tablets are the fundamental factors affecting patient compli- ance. In the case of liquisolid tablets, the attributes result from the dose of the API, its solubility in the solvent used, carrier and coating material absorptiv- ity and their weight ratio as well as polymer addi- tives to the formulation.
The aim of this study was to develop and opti- mize liquisolid tablets composition characterized by improved dissolution rate and possible small size and mass. Furthermore, the influence of various car- riers and carrier to coating material ratio were stud- ied in respect to the liquisolid tablets mechanical properties and model drug dissolution profile.
Furosemide, in the dose of 40 mg which is registered on the market, was chosen as a model practically insoluble in water drug substance which belongs to biopharmaceutical classification system (BCS) class IV (9). So far, liquisolid formulations containing 20 mg of furosemide were studied by Akinlade et al.
(7).
EXPERIMENTAL Materials
Furosemide in the form of micronized powder (J.B. Chemicals and Pharmaceuticals, India) was used as a model drug. Microcrystalline cellulose of various grades (VivapurÆ 102 and VivapurÆ 12), anhydrous dibasic calcium phosphate - Emcom- pressÆ Anhydrous (JRS Pharma, Rosenberg, Germany) and spherically granulated anhydrous
dibasic calcium phosphate FujicalinÆ (Fuji Chemical Industries, Toyama, Japan) were used as carriers, magnesium aluminometasilicate NeusilinÆ US2 (Fuji Chemical Industries, Toyama, Japan) as a coating material, crospovidone - KollidonÆ CL (BASF, Ludwigshafen, Germany) as a disintegrant and macrogol 400 (B.D.H. Chemicals) as a drug sol- vent.
Solubility studies
The solubility studies of furosemide were car- ried out in PEG 400 or in water. An excess amount of furosemide was added to 10 mL of solvent and shaken using a reciprocating shaker (IKA KS 130 BASIC, Germany) at 400 rpm for 24 h in room tem- perature to reach an equilibrium state. Then, the samples were centrifuged and filtered through a 0.45 µm Millipore filter, diluted and analyzed spec- trophotometrically (Jasco V-530 UV/Vis spec- trophotometer, Japan) at λ = 228 nm. All measure- ments were done in triplicate.
Excipients properties
The angle of repose was determined in accor- dance to Ph. Eur. 8.0 method by pouring the powder sample from the bottom sieve container mounted 70 mm above a round horizontal surface (60 mm dia.) until the cone was formed. The angle of repose was measured using measuring rod connected with the angular and metric scale. The angle of repose corre- sponds to the maximum angle between the slope of the formed cone and the horizontal surface. The attribute describes frictional forces in loose powder.
Bulk and tapped density were measured according to the European Pharmacopeia using a W-1 volume- ter (ZDM Polfa, Poland). Hausner ratio (HR) and Carrís index (CI) were calculated as follows:
Tapped density ñ Bulk density
CI = ñññññññññññññññññññññññññññ (Eq.1) Tapped density
Bulk density
HR = ñññññññññññññññ (Eq. 2) Tapped density
The moisture content was analyzed using a RadWag WPE 30S apparatus at 100OC and 15 s sampling time till the constant weight of the sample was achieved.
The flowable liquid retention potential (Φ) (Eq. 3) corresponds to the maximum amount of liq- uid that can be absorbed by the excipient, while pre- serving its good flowability (10). To obtain the liquisolid powder with good flow properties, the angle of slide of the excipients with admixture of increasing amounts of PEG 400 was investigated.
The sample of powder (1.0 g) was placed on a pol- ished metal plate which was gradually tilted until the
sample started to slide. In order to check physical properties of admixed ingredients the samples were examined 5 min and 24 h after preparation. Values of Φ were calculated for mixtures which slides down at the angle of plate inclination of 33O, which is considered to be optimal flow of the powder.
Wliquid
Φ = ññññññññññññ (Eq. 3) Wpowder
where: Wliquidñ weight of liquid, Wpowderñ weight of dry powder.
Preparation of liquisolid tablets
The composition of tablets is presented in Table 1. The maximum amount of furosemide solu- tion (liquid load factor Lf) which can be loaded into powder bulk was calculated according to equation 4 (10):
Lf= Φcarr.+ Φcoat (1/R) (Eq. 4) where: ñ liquid load factor, Φcarr., Φcoat.ñ flowable liquid retention potential for carrier and coating material, respectively, R ñ carrier/coating material ratio.
Twelve liquisolid formulations with four type of carriers: FujicalinÆ (LS1 ñ LS3), EmcompressÆ (LS4 ñ LS6), VivapurÆ 12 (LS7 ñ LS9) and VivapurÆ 102 (LS10 ñ LS12) were prepared. The each individual carrier was combined with different amount of coating material. In particular, the follow- ing carrier to coating material ratios were examined:
1 : 1, 5 : 1, 10 : 1. Tablets were prepared as follows,
the carrier was placed in a mortar and mixed with 20% furosemide solution in macrogol 400 poured in the quantity equal to 40 mg dose of the API. The coat- ing substance (NeusilinÆ US2) was gradually added and blended gently for 5 min. Then, 5% of KollidonÆ CL was added and mixing was continued for the next 5 min. Final blends were compressed using a Korsch EK0 single punch tablet press (Germany). Two lots of tablets (LS13 and LS14) were prepared using magne- sium aluminometasilicate in the function of carrier and coating material. The lots were differentiated by quantities of disintegrant as follows: 5% for the LS13 formulation and 10% for LS14.
Preparation of directly compressed tablets (DCT) Control tablets containing 40 mg of crystalline furosemide were prepared with direct compression method. The furosemide powder was mixed with suitable amounts of considered carrier and coating material. Afterwards, 5% of Kollidon Cl was added as a disintegrant and mixed. Final blend was com- pressed using Korsch EK0 (Germany) eccentric tablet press.
Evaluation of tablet properties
Tablet mass uniformity, thickness and hardness Ten tablets of each formulation were accurate- ly weighed and measured. The hardness of the tablets was evaluated using a VanKel VK 200 hard- ness tester (USA).
Table 1. Composition of prepared liquisolid tablets calculated on 100 tablets batch.
Coating 20% Kollidon Cl
Form. Carrier (Q) quantity [g] material furosemide amount R Lf
quantity [g] solution [g] [%]
LS1 11.2 11.2 1 1.793
LS2 Fujicalin 33.2 06.6 5 0.602
LS3 44.2 4.4 10 0.453
LS4 11.9 11.9 1 1.678
LS5 Emcompress 41.1 08.2 5 0.487
LS6 59.1 5.9 5% 10 0.338
LS7 12.7 12.7 20.0 1 1.574
LS8 Vivapur 12 52.2 10.4 5 0.383
LS9 85.4 8.5 10 0.234
LS10 13.2 13.2 1 1.510
LS11 Vivapur 102 62.7 12.5 5 0.319
LS12 117.5 11.8 10 0.170
LS13
Neusilin US2 13.4 5% - -
LS14 13.4 10% - -
Friability
The friability test was performed according to the European Pharmacopoeia 8.0 using PharmaTest PTF-E friabilator (Germany).
Disintegration time
Tablets disintegration time was determined using a disintegration test ElectroLab ED2 Sapo (India) apparatus in accordance with Ph. Eur. 8.0 method. Purified water kept at 37OC was used as a medium, six randomly selected tablets from each formulation were evaluated.
Furosemide content determination
Three randomly taken tablets of each formula- tion were accurately weighed and shaken with 200 mL of sodium hydroxide solution (4 g/L) over 24 h
(IKA KS 130 Basic shaker, Germany). Afterwards, samples were centrifuged at 3600 rpm and filtered through 0.45 µm MiliporeÆ filter. After dilution, drug concentration was assayed spectrophotometri- cally using a Jasco V-530 UV-Vis spectrophotome- ter (Japan) with a wavelength λ = 228 nm.
Dissolution studies
Drug dissolution studies were carried out using a Ph. Eur. 8.0 dissolution apparatus 2 (Hanson Research SR8 Plus Dissolution Test Station, USA) operated at 50 rpm. Tablets were placed in 900 mL of 0.1 mol/L hydrochloric acid solution (pH 1.2) at 37OC. Sample volumes of 5 mL were withdrawn from each dissolution vessel at 5, 10, 15, 30, 60 and 120 min and analyzed spectrophotometrically at λ = 228 nm. Every time vessel volumes were replen-
Table 2. Excipients parameters.
Excipient Φ value Humidity Angle of Hausner Carr index
content (%) repose (O) ratio (%)
Vivapur 102 0.021 4.7 45 1.38 27.7
Vivapur 12 0.085 2.5 38 1.39 28.3
Emcompress Anh. 0.189 0.6 34 1.21 17.0
Fujicalin 0.304 1.1 30 1.14 12.5
Neusilin US2 1.489 7.2 27 1.15 13.3
Table 3. Physical parameters, disintegration time and amount of drug dissolved of each formulation.
Average Amount of API Form. Tablet mass Dia. Thickness Hardness Friability
disintegration dissolved after
[mg] ± SD [mm] [mm] [N] ± SD [%]
time 2 h [%] ± SD
LS1 439.1 ± 8.6 10 4.07 45.6 ± 7.3 0.78 5 min 11 s 83.11 ± 5.77
LS2 627.7 ± 11.9 11 4.92 38.5 ± 2.4 0.13 1 min 58 s 92.93 ± 10.54
LS3 721.2 ± 6.3 12 4.25 48.4 ± 2.5 0.03 7 min 40 s 91.08 ± 7.29
LS4 463.7 ± 9.5 11 3.60 40.3 ± 5.5 0.31 9 min 07 s 85.17 ± 18.84
LS5 728.7 ± 8.1 11 4.68 51.3 ± 3.2 0.06 5 min 22 s 83.59 ± 14.06
LS6 833.8 ± 14.5 11 5.43 56.7 ± 9.1 0.08 1 min 26 s 84.79 ± 9.59
LS7 476.4 ± 8.7 15 3.74 40.6 ± 0.9 0.15 9 min 18 s 79.11 ± 15.53
LS8 870.0 ± 14.9 15 4.45 53.5 ± 9.3 0.15 29 s 69.27 ± 1.16
LS9 1200.0 ± 13.3 15 6.88 58.3 ± 4.5 0.97 26 s 71.09 ± 2.16
LS10 484.9 ± 5.8 12 3.68 48.2 ± 3.6 0.17 12 min 13 s 52.18 ± 17.66
LS11 1009.0 ± 11.2 15 5.75 53.6 ± 3.3 0.79 31 s 76.21 ± 0.49
LS12 1569.0 ± 34.1 20 4.93 48.5 ± 7.4 0.71 24 s 68.20 ±3.30
LS13 349.7 ± 5.6 10 3.88 36.2 ± 4.0 0.13 14 min 53 s 85.83 ± 6.55
LS14 360.0 ± 6.8 10 4.16 37.2 ± 5.7 0.14 7 min 51 s 95.86 ± 5.66
DCT 460.0 ± 7.1 12 4.21 58.35± 4.2 0.90 52 s 28.53 ± 2.30
ished automatically with fresh medium. The meas- urements were carried out in triplicate. There was no interference on the absorption spectrum of furosemide from liquid vehicles and other excipi- ents.
RESULTS AND DISCUSSION
The solubility of furosemide in macrogol 400 (234.97 mg/mL) was approximately 10000 times higher than in water (26.9 µg/mL). Javadzadeh et al.
(12) showed that the dissolution rate is directly pro- portional to the fraction of molecularly dispersed drug (FM) and the use of drug solution causes that the FM factor is as high as possible (FM = 1). The high solubility of furosemide in macrogol 400 allows obtaining small tablets since less amount of liquid has to be adsorbed onto powder surface.
According to the flowability results obtained for raw materials it was stated that NeusilinÆ US2 possesses the best flow properties (Table 2). Its flow characteristic can be expressed as excellent based on the angle of repose lower than 30Oand good accord- ing to the compressibility index (11-15%) and Hausner ratio (1.12 ñ 1.18). The results of the liquid sorption capacity show that the values of flowable liquid retention potential (Phi, Φ) were correlated with the angle of repose of raw material and it increases with lower angle of repose values. The Phi-values were in the range from 0.021 for VivapurÆ 102 up to 1.489 for magnesium alumi- nometasilicate, which corresponds with the highest angle of repose of VivapurÆ 102 (45O, passable flow - may hang up) and the lowest for NeusilinÆ US2 (27O, excellent flow) from all of tested excipi- ents. The high humidity content of NeusilinÆ US2 is due to its large specific surface area reaching up to 300 m2/g (11), but absorbing capacity was not affected by the humidity content, because Φ-value was the highest and reached up 1.49. The compari- son of EmcompressÆ and FujicalinÆ shows better flow properties of the spherically granulated dibasic calcium phosphate (FujicalinÆ). The difference between those excipients is in their specific surface area and shape. FujicalinÆ is composed of spheri- cally granulated particles with a porous surface which results in a high specific surface area, i.e., over 32 m2/g while EmcompressÆ Anhydrous has 20.7 m2/g (11) which resulted in approx 1.6-fold lower liquid sorption capacity. Also the microcrys- talline cellulose VivapurÆ 12 with a larger particles, of median size 180 µm, has a higher value of flow- able liquid retention potential in comparison to VivapurÆ 102 with an average particle size of 100
µm. Based on the comparison of obtained results it can be stated that the spherically granulated anhy- drous dibasic calcium phosphate is the most suitable carrier.
The characteristics of all kinds of tablets are presented in Table 3. Among the evaluated physical properties such as mass, thickness, hardness, friabil- ity and disintegration time for liquisolid formula- tions, the differences has been identified particular- ly in tablet mass and disintegration time. A relation- ship between the excipients properties and the tablets mass and diameter was identified. Tablets prepared with high absorption capacity substances such as magnesium aluminometasilicate (LS13, LS14) and spherically granulated anhydrous dibasic calcium phosphate i.e. formulations LS1ñLS3 have the lowest mass among of the studied formulations prepared with different types of carriers. When EmcompressÆ was used as a carrier the increase of tablet mass was estimated while disintegration time was elongated only for two formulations (LS4, LS5). Tablets with microcrystalline cellulose PH102 were characterized by the highest mass exceeding 1569 mg and use of punches with 20 mm in diame- ter (LS12). Similar results were obtained by Hentzschel et al. while replacing microcrystalline cellulose and silica with NeusilinÆ US2 causing the griseofulvin unit dose mass reduction from 2026 to 600 mg (8).
The tablets parameters also depend on carri- er/coating material ratio. The increase of NeusilinÆ US2 amount in the formulation results in the tablet mass and size decrease due to its high sorption capacity. For example, the mass of LS1 tablets con- taining 112 mg of NeusilinÆ US2, with the carrier to coating ratio 1 : 1, was 439 mg and 10 mm in diam- eter while in the case of LS3 tablets, in which the amount of NeusilinÆ US2 was three times lower, the tablet mass was 721 mg and diameter was 12 mm. The same relationship was identified for tablet formulations prepared with other carriers. Based on Ph. Eur. 8.0 monograph all of the tablets met the pharmacopeial friability requirement because the loss of weight after the friability test did not exceed 1%. The average disintegration time ranged from 24 s (LS12) to 14 min 53 s (LS13). Compared the aver- age disintegration times for tablets containing microcrystalline cellulose with different amount of NeusilinÆ US2 i.e., LS7 ñ LS12 tablets, it was stat- ed that high quantity of NeusilinÆ US2 in formula- tion significantly affect the disintegration time. This was confirmed by long disintegration times for tablets composed only with this coating material.
LS13 tablets do not comply with the pharmacopeia
requirement, despite that the average time was below 15 min but three of the six tablets had a dis- integration time over 15 min. Two-fold higher amount of the disintegrant in the LS14 formulation with respect to the LS13 tablets resulted in reduction of disintegration time by half (Table 3).
The effect of the excipients used in tablet for- mulations on furosemide release profile was investi- gated. As shown in Table 3, there were large differ- ences in drug dissolution between fourteen types of tablets. The amount of furosemide dissolved after 2 h was in the range from 52.18% to 95.86%. Taking into account tablet formulations prepared with both kinds of the excipients i.e., carrier and coating mate- rial (LS1 ñ LS12), the highest amount of the drug (92.93%) was released from LS2 liquisolid tablets containing spherically granulated anhydrous dibasic calcium phosphate (FujicalinÆ) as a carrier. In the case of EmcompressÆ, independently of excipients quantity the amounts of furosemide released after 2 h were similar 83.6% ñ 85.2% (formulations LS4 ñ LS6). The release profiles of furosemide for micro- crystalline cellulose based formulations varied depending on the physical properties of the carrier, and VivapurÆ to NeusilinÆ US2 ratio (Table 3).
The dissolution profiles of furosemide from tablets with 1 : 1 carrier/coating ratio (LS1, LS4, LS7) were similar independently from the kind of the carrier i.e., FujicalinÆ, EmcompressÆ and VivapurÆ 12. The only exception was the formula- tion with VivapurÆ PH102 (LS10). This kind of tablets differs in the physical properties and dissolu- tion of furosemide. They were characterized by long disintegration time, exceeding 12 min and the low- est amount of furosemide dissolved after 2 h
(52.2%). High quantity of NeusilinÆ US2 with its large specific surface area significantly influenced furosemide dissolution profile.
From these results it can be assumed that liquisolid tablets with FujicalinÆ and NeusilinÆ US2 are recommended to enhance the dissolution rate of furosemide. Two formulations LS2 and LS14 fully met the formulation expectations. The similar amount of furosemide was released from both LS2 and LS14 formulations after 2 h i.e., 92.93 and 95.86%, respectively. The mass of LS2 tablets was 627 mg, disintegration time 1 min 58 s. In compari- son, the mass of the LS14 tablets was the smallest one i.e., 366 mg but the disintegration time was 4- fold longer. As it is presented on Figure 1, the amount of dissolved drug after 2 h from liquisolid tablets was over 3-times greater than in control tablets (DCT).
CONCLUSION
This study showed that liquisolid technique is a promising strategy in the pharmaceutical technol- ogy. The formulation of liquisolid tablets enhances the dissolution rate of furosemide when compared with direct compressed control tablets. Typically used dose of furosemide is 40ñ120 mg a day but there was no study on 40 mg furosemide liquisolid tablets. The results of investigations demonstrate that by selection of suitable excipients 40 mg furosemide tablets with acceptable size and mass with fast and entire drug dissolution could be pre- pared. Spherically granulated dibasic calcium phos- phate (FujicalinÆ) and magnesium aluminometasil- icate (NeusilinÆ US2) as carrier and coating materi-
Figure 1. Comparison of furosemide dissolution profiles for the best liquisolid tablets and direct compressed control tablets
al, respectively, are suitable for liquisolid technique.
The optimized formulations LS2 and LS14 showed 86.5 ± 8.6% and 84.3 ± 11.4% drug release within first 30 min and 92.9 ± 10.5% and 95.9 ± 5.7% after 2 h, respectively. The improvement in the furo- semide dissolution characteristics from liquisolid tablets is mainly due to utilization of solution of the API. It was also stated that the dissolution profiles are affected by the amount of highly absorptive excipients such as NeusilinÆ US2. Other physical parameters such as hardness, friability and disinte- gration time were also satisfactory. The mass of both formulations was also reduced. It is an important factor that should be considered in aspect of patient compliance.
Acknowledgments
The research was supported by the Polish Ministry of Higher Education and Science as Grant No. K/DSC/002883 to development of young researchers at the Jagiellonian University, Medical College. One of the authors (Mohammad Hassan Khalid) is supported by the IPROCOM Marie Curie initial training network, funded through the People Programme (Marie Curie Actions) of the European Unionís Seventh Framework Programme FP7/2007- 2013/ under REA grant agreement No. 316555.
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Received: 6. 10 2015
